Subaqueous gravity flows (SGF) including sediment-laden turbidity currents are quite common in nature and are important both in transporting land materials into lakes, oceans and also in shaping the subaqueous morphology. By checking the flow thickness versus specific energy curves of SGF undergoing from 0.5° to 10° seven slop transitions for the first time, it is surprising to find that: i) contrary to popular thinking, SGF on most part of the slope with Froude number larger than unity are not supercritical; ii) there are two inflection points on the thickness-energy curves, indicating SGF are supercritical only in short regions around the inlet and slope transitions, something like open channel flows undergoing a sluice gate; iii) the critical Froude number of those SGF are well above unity corresponding to weaker internal hydraulic jumps than their cousins in open channel with unity critical Froude number; iv) the higher the slope transition, the wider the supercritical flow region. These findings may assist us in understanding the mechanisms of some subaqueous topography relating with subaqueous gravity flows.